Method of producing suede-like artificial leathers

ABSTRACT

A PROCESS FOR PRODUCING SUEDE-LIKE ARTIFICIAL LEATHERS WHICH COMPRISES COATING A SOLUTION OF A POLYMER ONTO A FIBROUS BASE MATERIAL, SUPERIMPOSING A FLOCK ON A CARRIER SHEET ON THE POLYMERIC COATING LAYER, SUBJECTING THE RESULTING COMPOSITE SHEET TO TREATMENT WITH A COAGULATION LIQUID AND, AFTER COAGULATION OF THE COATING LAYER INTO A MICROPOROUS STRUCTURE, REMOVING THE CARRIER SHEET FROM THE FLOCKED SHEET MATERIAL.

United States Patent 3,573,121 METHOD OF PRODUCING SUEDE-LIKE ARTHFHCIAL LEATHERS Kazuo Fukada, 851 Z-chome, Aza-Nagaoyama, Hyogo, Japan; and Hiroshi Okamoto, 124,0 Shimo-Chujo-cho, Ibaragi-shi; and Yoshihilro Numata, 4-1 Tsukimi-cho, Takatsuki-shi, both of Osaka, Japan No Drawing. Filed Apr. 8, 1968, Ser. No. 719,713 Claims priority, application Japan, Apr. 6, 1967, 42/22,045 Int. Cl. B3211 5/18 U.S. (ll. 156-77 6 Claims ABSTRACT OF THE DISCLOSURE A process for producing suede-like artificial leathers which comprises coating a solution of a polymer onto a fibrous base material, superimposing a flock on a carrier sheet on the polymeric coating layer, subjecting the resulting composite sheet to treatment with a coagulation liquid and, after coagulation of the coating layer into a microporous structure, removing the carrier sheet from the flocked sheet material.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to a method of producing suedelike artificial leathers.

DESCRIPTION OF THE PRIOR ART Various investigations and developments have been made relating to the manufacture of suede-like artificial leathers. Some of the prior methods utilized have obtained artificial leathers having a suede-like touch to the hand and the external appearance of suede by a two-step process which comprises forming a coating layer of a porous polymer by a foaming, coagulating or leaching-out process and then scraping off the surface skin of the so formed polymeric porous coating layer. Other methods utilize piles which have been deposited on a sheet material by a flocking process to gain the feel.

Suede-like artificial leathers obtained by prior methods have characteristics which are dependent on the method employed. These leathers are of commercial value, but prior methods have certain inherent defects, for example, the products obtained do not always have satisfactory physical properties, such as touch to hand, external ap' pearance and other characteristics desirable in artificial leather.

For example, with the polymeric porous coating processes described above, it is difficult to obtain a polymeric coating layer in which the pores are uniformly distributed in all three dimensions, and the surface obtained by scraping the surface skin from the resultant coagulated polymeric coating layer thus often consists of thin walled pores or cells. This does not have a slippery touch to the hand like natural leather.

In the flocking method described, it is possible to obtain products having variable physical properties (such as touch to hand and/or external appearance) by appro priate choice of the base material, binder and/ or the pile. However, the product has a fatal defect in that it is significantly inferior in airand moisture-permeability when compared to natural leather.

SUMMARY OF THE INVENTION The inventors have discovered a novel process which enables an artificial suede-like leather to be produced which has excellent moisture and air permeability, abrasion resistance and a suede-like touch to the hand. The external appearance is also very pleasing, and closely resembles natural leather.

The invention basically comprises coating a solution of a soft polymer onto a fibrous base material, superimposing a flock on a carrier sheet over the coating layer of the polymer solution and treating the composite sheet thus formed with a coagulation liquid in order to co agulate the polymeric coating layer into a microporous structure. The carrier sheet is then stripped from the flock.

The pore size obtained by the practice of the process of the present invention is generally uniform in all three dimensions, and the final characteristics of the product may be controlled by appropriate selection of the polymer utilized, the concentration of the polymer solution selected and the composition and temperature of the coagulation liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention overcomes defects inherent in the prior methods of producing artificial leathers and en ables the production of an artificial leather having excellent moisture and air permeability, abrasion resistance, a suede-like touch to hand and an external appearance of natural suede.

The present invention involves a process of producing suede-like artificial leathers which comprises coating a solution of a soft polymer onto a fibrous base material, superimposing a flock on a carrier sheet over the coating layer of polymer solution, treating the so formed comr posite sheet with a coagulation liquid in order to coagulate the polymeric coating layer into a porous structure and stripping the carrier sheet from the flock.

The soft polymers acceptable in the practice of the invention include N-isopropylated poly(hexamethylene adipamide), N-methoxymethylated poly(capramide) and similar N-substituted polyamides; block polyamides of poly(capramide) with poly(hexamethylene adipamide), poly(ethylene sebacate terephthalate) and similar copolymers; natural and synthetic rubbers; and inherently soft polymers.

In addition, polymers that are essentially rigid, but which may be rendered soft by plasticization, such as 6-nylon, 66-nylon, polyvinyl chloride, acrylonitrile copolymers and the like, are acceptable. Those polymers obtained by the chain extension of a substantially bifunctional poly(alkylene ether), polyacetal or polyester component (having as terminal groups isocyanates, acid halides, carbamyl halides or urea groups) with a bifunctional compound containing active hydrogen atoms are most suitable in the practice of the present invention. The bifunctional compound which contains active hydrogen atoms which is used as the chain-extender may be exemplified by water, ethylene glycol, diethylene glycol, propylene glycol, hydrazine, ethylenediamine, propylenediamine, tetramethylenediamine, xylidenediamine and the like. An example of such a polymer which is well known in the art is a polyurethane elastomer, which is most preferred in the practice of the present invention. The term polyurethane elastomer as used in this specification includes the so called polyurea elastomers or polyurethane-urea elastomers which may be prepared by reacting a hydroxy-terminated linear polymer with an organic diisocyanate and, optionally, a chain extender. A chain extender may be included in the state of a prepolymer in solution or in a block containing no solvent, although this is not necessary.

The hydroxy-terminated linear polymer may be exemplified by polyester glycols obtained by reacting a dicarboxylic acid compound with a molar excess of a glycol compound, polyester glycols obtained by the chain opening polymerization of a cylic ester, polyalkylene ether glycols obtained from a cyclic ether compound, and polyacetal glycols obtained by the polymerization of an aldehyde.

As the organic diisocyanate there may be used any of the organic diisocyanates which are usually used in the preparation of urethane elastomers, such as tolylene diisoyanates, naphthalene diisocyanates, diphenylmethane diisocyanates, hexamethylene diisocyanates, and the like.

As chain extenders the compounds listed above may be used.

Polymer solutions, in which one or more of these polymers are dissolved, may be formed.

A suitable polymer solvent, such as acetone, tetrahydrofuran, acetonitrile, N,N-dimethyl-formamide, N,N- dimethylacetamide, methanol, m-cresol or formic acid, may even be applied to the fibrous base material. The solution may be applied by any ordinary coating process, such as by doctor knife, roll coater, calendaring machine, extruder and the like.

Fibrous base materials which may be used include Woven, knitted and non-woven fabrics, paper and other fibrous sheet materials, especially fibrous Webs, nonwoven fabrics obtained by needle punching a fibrous Web with a needle loom and composite sheets obtained by needle punching a laminate of a woven fabric with a fibrous web. The most preferred base materials in the practice of the present invention are those obtained by applying a polymeric material to a sheet material utilizing any standard process.

After the application of a solution of a soft polymer, a flocked sheet material is superimposed over the fibrous base material in such a manner that the flocked side of the flocked sheet material is contacted with the coating layer of the polymer solution. The resultant assembly or laminate is treated with a coagulation liquid in order to coagulate the layer of applied polymer solution.

The treatment with the coagulation liquid is, in general, effectively performed by soaking the assembly in a bath containing the coagulation liquid, though it may be performed by spraying the liquid on the assembly or by exposing the assembly to the coagulation liquid in vapor form.

It is essential that the coagulation liquid be miscible With the solvent in the polymer solution which has been applied to the fibrous base material. Typical coagulation liquids include, for instance, water, methanol, ethanol, ethylene glycol, glycerol and the like.

The flocked sheet material may generally be prepared by flocking a carrier sheet using an adhesive which is soluble in either the solvent in the polymer solution or the coagulation liquid. The carrier sheet should be such that it is unaffected by both the solvent and the coagulation liquid. The carrier sheet has a great influence on the surface smoothness of the product. For instance, plane fabrics formed of a rayon or polyester fiber of low denier are suitable as the carrier sheet. Synthetic resin films, paper and metallic foils or sheets may also be suitably used as the carrier sheet. An adhesive used in the electrostatic flocking of the carrier sheet is preferably one which contains, as the main component, an easily soluble polymer, such as polyvinyl alcohol, polyacrylic acid derivatives, maleic anhydride-vinyl acetate copolymers, carbomethoxymethylcellulose and the like.

It will be necessary to select a proper adhesive composition in view of the type of solvent in the polymer solution being applied to the base material and the composition of the coagulation liquid used. In cases where a synthetic resin film or a metallic foil or sheet is used as the carrier sheet, it is especially necessary to use an ad- 4 hesive having particularly good solubility because of the impermeability of the carrier web differ markedly from the case when woven fabrics and similar porous sheet materials are used. In this case, it may be desirable to apply a release agent to the carrier sheet prior to flacking.

In general, the polymer solution may be cast into a film and soaked in a liquid which is miscible with the sol vent in the polymer solution but which is a non-solvent for the polymer in the polymer solution. A coagulation film will be formed on the surface of the film which is in contact with the non-solvent liquid and, thereafter mutual penetration and diffusion of the solvent in the polymer solution and non-solvent liquid takes place through the surface coagulation film which has semipermeable properties. Movement of the polymer solution in the contiguous inner portion of the layer of the polymer solution also takes place. In the inner portion of the filmy cast layer of the polymer solution, coagulation of the polymer occurs by the action of the non-solvent liquid penetrating from the outer side. The coagulation thus starts from hte surface layer and gradually extends to the inner portion of the filmy cast layer, thereby forming a polymer concentration gradient in the polymer solution layer which will act as a driving force, promoting internal diffusion of the solvent.

The coagulated film often assumes a structure which has a nonuniform pore size and distribution, since the penetration, diffusion and movement of materials in the inner portion of the cast layer may proceed very irregularly. During the course of coagulation of a homogeneous polymer solution, if a pile which is uniformly distributed is present throughout the layer of the polymer solution, the pile acts as a nucleus or center of coagulation, and leads to the formation of a porous layer of very uniform structure.

After substantially complete coagulation of the applied coating layer of a solution of soft polymer, the carrier member of the flocked sheet is removed, leaving the pile in the coagulated polymer layer. Thus, there is formed a coagulated polymeric layer which has a suede-like surface which comprises the thin walls of uniform cells and uniformly distributed piles substantially perpendicular to the plane of the base material.

The microporous structure of the coagulated polymeric layer is somewhat dependent on the type of pile used, but it is influenced to a greater extent by the form, moisture content and other physical characteristics of the pile. However, the touch to hand, texture and physical properties of the final product can be varied by the proper choice of the type of pile. Accordingly, in the practice of the present invention, suede-like artificial leathers of different textures may be obtained by the selective use of various flocks, either alone or mixtures thereof, such as flocks of cotton, linen, silk, wool or similar natural fibers; rayon, acetate or similar semi-synthetic fibers; nylon, polyester, polyacrylic fiber or similar synthetic fiber; or milled pulp or milled leather.

The cellular structure of the coagulated polymeric layer has a great influence on the touch to the hand, texture and physical properties of the final product. In general, where a polymer solution is coagulated in the form of a cast film into a cellular or porous layer, the resulting cellular structure varies depending on the kind of polymer, the kind and concentration of the solution, and the composition and temperature of the coagulation liquid and other coagulation conditions. For example, if coagulation is conducted under identical conditions, a homogeneous polymer solution, a heterogeneous polymer solution (prepared by the addition of a small amount of a non-solvent to a homogeneous solution) and a polymer solution prepared by incorporating insoluble particles of an organic polymer or inorganic substance in a homogeneous or hetergeneous polymer solution as described above, will give coagulated polymeric layers having remarkably different porous structures.

Thus, in the practice of the present invention, it is possible to produce a wide variety of suede-like artificial leathers by appropriate selection of the various factors which have a direct influence on the cellular structure of the coagulated polymeric layer.

After the removal of the carrier member of the flocked sheet material, the coated product is subjected to drying. The drying may be conveniently performed using a hot airrecirculating drier. It is important that the solvent in the coated product be substantially eliminated from the coated product prior to drying, since any remaining solvent will cause the heat distortion temperature of the polymer to be lowered, and may thereby cause a collapse of the micropores formed during the preceding coagulation step.

The dried product thereby formed may be used as a suede-like artificial leather in the manufacture of shoes, bags, hand-bags, apparel or upholstery. In certain uses the product may be buffed or treated with a water-repellent or antistatic agent in order to impart thereto the desired property. The product of the present invention may be colored by the addition of a dye or pigment in the polymer solution or by deying the final product.

The present invention will be now illustrated in more detail by the following example which is merely illustrative and is not to be taken as limiting.

EXAMPLE A composite fibrous sheet material used as the base material was formed by superimposing a web of nylon staple of 3 den. x 51 mm., having a weight of 200 g./m. on a cotton flannel, having a weight of 180 g./m. and subjecting the resulting assembly to needle punching from the side of the web by means of needle loom.

Alternatively, a prepolymer, derived from 1 mol of polypropylne glycol (with an average molecular weight of 1,000) and 2 mols of diphenylrnethane diisocyanate (having a free isocyanate content of 5.44%) was dissolved in N,N-dimethylformamide (hereinafter referred to as DMF). To the resulting solution there was added, while stirring and maintaining the solution at C., a polyether-urethane-urea elastomer equivalent to the free NCO of hydrazine hydrate a DMF solution. The solution was diluted with DMF to a polymer content of 10%, and the composite fibrous sheet material was impregnated with the diluted solution, coagulated in an aqueous bath, washed with water and dried to obtain a flexible sheet material having a weight of 410 g./m. and a moisture permeability of 3,760 g. H O/24 hr./m.

A solution in DMF of the polyether urethaneurea elastomer prepared in the manner described above, having a viscosity at 23 C. of 5,500 cps., was applied to the sheet material by means of a doctor knife to form a coating layer of about 1 mm. thickness. A flocked sheet material was superimposed over the coating layer in such a manner that the flocked side came into contact with the coating layer. The flocked sheet material was prepared by applying an emulsion-type adhesive (containing as the main component, a copolymer of 60% ethyl acrylate and 40% butyl acrylate) to a plane fabric formed of rayon staple yarns, and electrostatically depositing thereon a mixed flock of 0.5 den. x 0.8 mm. of rayon and 60% nylon.

The assembled coated sheet material and flocked sheet material was soaked in water at 30 C. for 20 minutes and then soaked in warm water at C. for 30 minutes. During this treatment the carrier sheet (rayon plane fabric) became easily removable from the assembly, and upon removal left the flock. The coated product was, after removal of the carrier sheet, soaked in warm water at 70 C. for 1 hour with 10 squeezings, utilizing squeeze rolls. Thus, the DMF was substantially completely extracted from the coated product. The coated product was then dried in a hot air-recirculating drier to obtain an artificial leather of a suede-like external appearance and touch to the hand having the following physical properties:

Custom fold wear (JISL1004) (Emery paper #600,

load 1 lb./2.5 cm. width)-30O times Scott type folding and abrasion test (JISL1005)- 30,000 times Moisture permeability-850 g. H O/ 24 hr./m

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of producing suede-like artificial leathers which comprises (a) coating a solution of a soft polymer onto a fibrous base material to thereby form a coating layer,

(b) superimposing a flock on a carrier sheet on the polymeric coating layer,

(0) subjecting the resulting composite sheet to treatment with a coagulation liquid and in order to thereby coagulate the coating layer into a microporous structure, and

(d) removing the carrier sheet from the flocked sheet material.

2. A method as in claim 1 in which the coagulation liquid is water.

3. A method as in claim 1 in which the treatment with a coagulation liquid is performed by soaking the composite sheet in a bath containing the coagulation liquid.

-4. A method as in claim 2 in Which the coagulation liquid is water.

5. A method as in claim 2 in which the soft polymer is a poly-urethane elastomer.

6. A method as in claim 2 in which the solution of soft polymer comprises a solution of a polyurethane elastomer in N,N-dimethyl formamide.

References Cited UNITED STATES PATENTS 3,387,989 6/1968 West et al 117-76 FOREIGN PATENTS 144,148 1962 U.S.S.R. 156-77 1,096,583 12/1967 Great Britain.

LELAND A. SEBASTIAN, Primary Examiner UJS. Cl. X.R. 

